Spark plug with a center insulator which covers the end of the shell



Jan. 6, 1970 F. w iG 'r '3 ,488.545

SPARK PLUG WITH A CENTER INSULATOR WHICH covsns THE END OF THE SHELL File 01 Oct. 25. 1967' 36 28 22 INVENTOR.

l8 GILBERT F. WRIIGHT 20 I9 BY v V ATTORNEYS United States Patent 3,488,545 SPARK PLUG WITH A CENTER INSULATOR WHICH COVERS THE END OF THE SHELL Gilbert F. Wright, 511 Carlyn Court, Sunnyvale, Calif. 94086 Filed Oct. 23, 1967, Ser. No. 677,458 Int. Cl. H01t 13/20 U.S. Cl. 313-143 12 Claims ABSTRACT OF THE DISCLOSURE A spark plug having a central core of insulating material mounted in an outer tubular body with the core having a tubular extension surrounding and spaced from the nose portion of the core and an annular lip projecting laterally from the extension. The extension thermally isolates the adjacent inner surface of the body and the lip thermally isolates the adjacent end face of the body. Heat dissipation to an engine block is across a gasket between the core and the body at a location spaced from the nose portion. Improved structure is provided to hold the core fixed relative to the body.

This invention relates to improvements in spark plugs for use in internal combustion engines, and more particularly to an improved spark plug whose central insulating core is shaped to provide greater heat dissipation to an engine block.

The present invention is directed to an improved spark plug whose central core has a unique configuration for maintaining the mounting body or shell in which the core is disposed at a relatively low operating temperature while assuring that the nose portion of the core surrounding the central electrode will be maintained at a temperature sufiicient to avoid fouling and pre-ignition at the nose portion. To accomplish this, the core has its nose portion surrounded by a tubular extension to form an annular recess sufficiently deep to collect combustion gases by means of which the nose portion will be readily heated to the desired non-fouling temperature. Also, the core has a lateral projection or lip integral with the extension to cover or shield the proximal end face of the mounting body. Thus, the extension thermally isolates the portion of the inner surface of the body near the combustion zone and the lip thermally isolates the adjacent end face of the body whereby combustion gases will remain substantially out of contact with these surfaces and the body will remain at a relatively low temperature during continued operation of the spark plug. This low temperature condition of the body is achieved even through the nose portion of the core continues to operate at a temperature between the non-fouling minimum temperature and the preignition temperature.

Conventional spark plugs are generally classified as hot plugs and cold plugs for use with cold engines and hot engines, respectively. Hot engines are constructed to provide for smaller heat dissipation from the nose portion of the spark plug to the engine block than is capable with cold plugs. Thus, hot plugs are operated at a higher tip or nose portion temperature than cold plugs for a given combustion chamber temperature. For optimum performance, the tips of plugs should operate at approximately the same temperature. Thus, hot plugs are used with cold running or low performance engines and cold plugs are used with hot running or high performance engines.

Two temperature parameters which are of important: in the proper design of spark plugs are the non-fouling temperature and the pre-ignition temperature of the insulator material at the nose portion of the core of the ice spark plug. The non-fouling temperature typically should be in the range of approximately 900 F. and 1300 F. to avoid non-fouling, i.e., to avoid carbon and lead deposits on the nose portion. Above approximately 1700 F., with presently available fuels, pre-ignition will generally occur. Thus, the optimum configuration of a spark plug for a typical engine will provide for a minimum operating temperature of at least 900 F. and a maximum operating temperature of 1700 F. at the nose portion. There may be variations in these parameters for certain types of engines so that only typical values have been set forth.

Commercially available hot and cold spark plugs generally operate in relatively narrow temperature ranges. Thus, they are limited in their uses to specific applications. For instance, a hot plug, i.e., one with a relatively long nose portion, when designed for use with low grade fuels or with a cold engine, has a tendency to cause preignition when high grade fuels are used or during hot weather when outside temperatures are cold. This is be cause the pre-ignition temperature is readily reached. A cold plug, i.e., one with a relatively short nose portion, when designed for use with high grade fuels or with a hot engine, tends to foul when lower grade fuels are used or during cold weather operation. This is due to the fact that the nose portion takes a relatively long time to reach the maximum non-fouling temperature of approximately 900 F.

The present invention avoids these problems by providing a spark plug capable of efficiently operating over a wider range of combustion chamber temperatures than is capable with conventional spark plugs. Thus, the spark plug of this invention can be used with both hot and cold running engines. This end is achieved by the specific construction of the central insulating core of the spark plug wherein the core is shaped to assure that the nonfouling temperature is quickly reached but that the preignition temperature is not attained for both high and low performance engines.

Specifically, the core has its nose portion and the surrounding tubular extension disposed to be readily contacted by the combustion gases, whereby the nose portion is rapidly raised to the minimum non-fouling temperature for cold engine operation. Thus, the nose portion, the tubular extension, and the annular recess therebetween give the plug its hot plug characteristics.

The tubular extension and the laterally projecting lip keep the mounting shell or body at a relatively low temperature by shielding it from the combustion gases. This provides a steeper or higher temperature gradient between the core and the body and assures greater heat dissipation from the core to the engine block to thereby provide the cold plug characteristics.

The primary object of this invention is, therefore, to provide an improved spark plug which has a central core shaped to assure that the nose portion surrounding the central electrode of the plug will, at all times during operation, be contacted by the combustion gases while the mounting body of the plug will be effectively shielded from such gases and thereby kept relatively cool, so that the nose portion will be quickly raised to and maintained at a non-fouling temperature while the temperature gradient between the core and the mounting body will be relatively high to assure that the pre-ignition temperature of the nose portion will not be' reached.

A further object of this invention is to provide a core for a spark plug which effectively isolates the end face and the adjacent inner surface of the mounting shell or body of the plug from combustion gases without impairing the exposure of the nose portion to the combustion gases so that the temperature gradient between the core and the mounting body will normally be at a relatively high value to thereby assure maximum heat dissipation between these two components while the nose portion is kept at or above the minimum non-fouling temperature- A further object of the invention is to provide an improved mounting body for a spark plug of the type described wherein the body is shaped to permit the core to be inserted therein'to at the end adjacent to the spark gap, whereby the shielding lip of the core can be made integral with the core itself and the spark plug can be readily assembled even when the ground electrode is attached to the mounting body.

Other objects of this invention will become apparent as the following specification advances, reference being had to the accompanying drawing for an illustration of the preferred embodiment of the invention.

In the drawing:

FIG. 1 is a view, partly in section, of a spark plug forming the subject matter of this invention;

FIG. 2 is a cross-sectional view taken along line 22 of FIG. 1; and

FIG. 3 is an end elevational view of the spark plug, partly in section, at the end corresponding to the spark gap thereof.

The improved spark of the present invention is broadly denoted by the numeral and includes a core 12 and a mounting shell or body 14 which removably receives core 12. Body 14 has a threaded sleeve 15 adapted to be threadably mounted on an engine block 16 of an internal combustion engine so that tip 18 of a central electrode carried by core 12 and one end of 19 of an L-shaped electrode 20 secured in any suitable manner to the proximal end face 22 of body 14 will form a spark gap in a cylinder of engine block 16.

Core 12 may be formed from any suitable insulating material normally used for cores of spark plugs, such as a ceramic having aluminum oxide as an ingredient. Also, body 14 is preferably formed from a metallic material to provide an electrical conduction path between electrode 20 and engine block 16. However, body 14 can be formed from other materials so long as the aforesaid electrical path is established- Also, body 14 should have a sufiicient mechanical strength to mount core 12 on engine block 16 and thereby position electrodes 18 and 20 within the corresponding combustion chamber thereof. Thus, a spark produced across the gap between the electrodes will ignite the-fuel mixture in the chamber.

Core 12 is provided at one end thereof with a generally cylindrical nose portion 26 which surrounds the proximal portion of the central electrode and from whose end face 28 electrode tip 18 projects. Core 12 also includes a tubular extension 30 which is spaced from and surrounds nose portion 26 (FIG. 1) to present an annular recess 32 extending inwardly a predetermined distance from end face 28. Also, a continuous lateral projection or annular lip 34 is integral with the outermost extremity of extension 30 and is disposed to cover or shield substantially the entire end face 22 of body 14. A small area of face 22 due to the end thread thereof may not be fully covered or shielded by lip 34. However, this area will be small enough to be substantially negligible.

Lip 34 has a notch 36 therein for clearing electrode 20 as shown in FIGS. 1 and 3. Initially, electrode 20 will be straight to allow core 12 to be inserted into the threaded end of body 14. When core 12 is positioned in body 14 as shown in FIG- 1, electrode 20 is then bent into its final L-shaped configuration and forms the spark gap with electrode 18.

The longitudinal portion 38 of core 12 next adjacent to nose portion 26 has a maximum transverse dimension greater than the centrally disposed longitudinal portion 40 remote from nose portion 26. Thus, portions 38 and 40 present an annular inclined shoulder 42 on which a metallic gasket 4 is disposed. Gasket 44 provides a heat conduction path between core 12 and body 14, whereby heat is dissipa ed o engine block 16. G sket 16 is of any suitable material having a high thermal conductivity, such as copper or the like.

The outer surface of extension 30 and the outer surface of longitudinal portion 38 are spaced inwardly from the inner surface 46 of the threaded sleeve 15 (FIG. 1) and lip 34 is spaced outwardly from end face 22. These spaces thus position the proximal end of core 12 out of contact with the body so that there will be essentially no heat exchange between the body and the core at these locations. Thus, the heat exchange path or heat conduction path between core 12 and body 14 will be through gasket 44 so that the heat will flow from core 12 transversely through the upper part of threaded sleeve 15 and into engine block 16 which will be Water cooled or air cooled, depending upon the type of engine with which spark plug 10 is associated.

The outer surface of longitudinal portion 40 is generally cylindrical and is integral at an annular zone 48 with a tapered or conical longitudinal portion 50 which extends toward the opposite end 52 of core 12.

The end of body 14 opposite to threaded sleeve 15 is provided with a number of spaced, longitudinally extending slots 54 separating the body into a number of transversely arcuate wall sections 56 which are shiftable radially outwardly of the longitudinal axis of the body 14. The inner surface of each wall section 54 has a projection 58 (FIG- 1) which is substantially complemental to the tapered longitudinal portion 50 of core 12 and has its maximum thickness at a location adjacent to zone 48 (FIG. 1). Thus, projections 58 present a substantially annular holding means which effectively retains core 12 in body 14 and prevents movement of the core out of body 14 through the threaded end thereof.

A retainer ring 57 is placed over wall sections 54 to hold the wall sections in juxtaposition to or against the outer surface of tapered portion 50. This ring is placed over the body after core 12 is inserted therewithin. To facilitate the mounting of the ring on the wall sections, the ring has a tapered inner surface 59 (FIG. 1).

Body 14 is provided with tool engaging flat surfaces 60 which form a hexagonal configuration for the outer surface of the body. Thus, these surfaces, as on conventional spark plugs, facilitate the insertion and removal of the spark plug from the engine block.

In assembling the spark plug, electrode 20 is formed from a bendable material and is initially straight. It is bent into the L-shaped configuration shown in FIG. 1 after core 12 is inserted into the body.

Since lip 34 is integral with core 12, the core must be inserted in body 14 through threaded sleeve 15. Since the outermost end 52 of core 12 has a greater diameter than longitudinal portion 40, the core will initially force wall sections 54 radially outwardly until tapered longitudinal portion 50 is in the position shown in FIG. 1. Then, the resilience of wall portions 54 return the latter to their normal positions with projection 58 in juxtaposition to and extending along tapered portions 50. In this way, longitudinal portion 40 of core 12 serves as a depression for projections 58. When this core is positioned in body 14 as shown in FIG. 1, lip 34 will be in proximity to and spaced from end face 22 and the shoulder 42 will force gasket 44 against the corresponding shoulder of body 14. Projections 58 will prevent reverse movement of core 12 and will effectively hold the latter against any substantial relative movement with respect to body 14. To hold wall sections 56 in place, ring 57 is placed over the same and forced into the position shown in FIG. 1. Electrode 20 is then bent into the shape as shown in FIG. 1, whereupon the assembly of spark plug 10 is complete. The spark plug is then ready to be mounted on engine block 16 and, when inserted in the manner shown in FIG. 1, body 14 is essentially isolated from the combustion gases created in the corresponding cylinder. This feature therefore maintains the temperature gradient between core 12 and body 14 at a relatively high value,

The configuration of core 12 allows gasket 44 to operate at a much lower temperature than that of the corresponding gasket in a conventional spark plug. The reason for this is that conventional spark plugs do not utilize any shielding of the inner surface of the threaded portion of the mounting body or any shielding of the corresponding end face of the body. While extension 30 and lip 34 will be exposed to the combustion gases, they will have a relatively low thermal conductivity so that there will be essentially no heat transfer from these components into the spaces adjacent to threaded sleeve 15. However, the outer surface of nose portion 26 will be exposed to combustion gases and this is to be desired to maintain the operating surface temperature at nose portion 26 above the non-fouling temperature, which is typically of the order of 900 F. The combined surface area of nose portion 26 and extension 30 need not be greater than the area of the nose portion of conventional plugs. The length of nose portion 26 can be shorter than that of a conventional plug because of the presence of tubular extension 30. Thus, the construction of core 12 provides for shielding the inner surface 46 without requiring an equal surface area of additional insulating material.

The spacing of extension 30 and longitudinal portion 38 from surface 46 keeps sleeve as cool as possible and thereby confines the heat transfer path between core 12 to body 14 at gasket 44. The spacing between extension and surface 46 should be as small as possible to prevent any fiow of gases in this region and to avoid heating the inner end surface 46 and thereby gasket 44. By making this spacing of a value in the range of 1 mil and 10 mils (1 mil equals .001 inch), this objective can be achieved.

The depth of recess 32 should also have a fixed value and for standard engine operation this depth is approximately inch and, for operations which normally require cold plugs, this depth can be approximately inch. For operations requiring hot plugs, this depth is preferably W inch.

The width of recess 32 should preferably be in the range of mils to 70 mils with the average being about mils. If the width is less than 40 mils, there will be insuificient space for the combustion gases to enter and to heat nose portion 26 to the required non-fouling temperature. If the width is greater than 70 mils, the thickness of extension 30 becomes too small to provide the required strength. Preferably, the width of recess 32 is the same as the thickness of extension 30 and this, in turn, is preferably equal to the wall thickness of nose portion 26.

The spark plug of the present invention will operate properly at both relatively low and relatively high combustion temperatures and also at combustion temperatures between relatively high and low values. Thus, the plug has a much wider operating range than conventional spark plugs. For cold engine operation, nose portion 26 is directly exposed to the combustion gases and will quickly reach the required minimum fouling temperature. The heating step is aided by the proximity of extension 30 to nose portion 26. During hot engine operation, gasket 44 remains relatively cool which results in a relatively high gradient between core 12 and body 14. This temperature gradient facilitates heat conduction to engine block 16 and this effect is very significant when core 12 becomes quite hot since the rate of heat conduction is proportional to the temperature gradient across gasket 44. In conventional spark plugs, the gasket corresponding to gasket 44 operates at a relatively high temperature causing the temperature gradient to be relatively low. In this way, the heat cannot be rapidly dissipated for eflicient operation and as a result, the range of the spark plug is seriously limited.

While one embodiment of this invention has been shown and described, it will be apparent that other adaptations and modifications can be made without departing from the true spirit and scope of the invention.

What is claimed is:

1. A spark plug comprising: a tubular shell having a pair of opposed, open ends with one of the ends having an end face; a central core disposed Within the shell and provided with a nose portion and a tubular extension at the extremity thereof adjacent to said one end of the shell, said extension being in surrounding, spaced relationship to said nose portion and being in proximity to and extending along the inner surface of said one end of the shell; means carried by said extension for substantially covering said end face of said shell, said core being in heat exchange relationship with said shell at a location spaced from said nose portion; and electrode means carried by said one end of the shell and said nose portion for defining an electrical spark gap therebetween.

2. A spark plug as set forth in claim 1, wherein said extension is spaced from said inner surface of the shell and said covering means is spaced from said end face.

3. A spark plug as set forth in claim 1, wherein said covering means includes a continuous lip integral with said extension.

4. A spark plug comprising: a core having a pair of opposed extremities and formed from an insulating material, said core having a nose portion and a tubular extension at one extremity thereof, said extension being spaced from and surrounding said nose: portion; a tubular body of electrically conductive material disposed on the portion of said core corresponding to said one extremity and having an outer end face and an inner surface extending inwardly from said end face and along and in proximity to said extension; means extending laterally from the extension for covering the end face of said body; means placing said body and said core in heat conduction relationship at a location spaced from said nose portion; a first electrode carried by said core and terminating at said nose portion; and a second electrode carried by said body at said one end and terminating at a region in proximity to said first electrode to present a spark gap therebetween.

5. A spark plug as set forth in claim 4, wherein said inner surface and said end face of the body are spaced from the extension and said covering means respectively.

6. A spark plug as set forth in claim 4, wherein said covering means includes an annular lip having a notch therein for clearing the adjacent portion of said second electrode.

7. A spark plug as set forth in claim 4, wherein said body is removably mounted on said core and provided with means for preventing any substantial relative movement between the body and the core.

8. A spark plug as set forth in claim 4, wherein said body has a number of slots extending thereinto from the opposite end thereof to present a plurality of relatively shiftable wall sections, the outer surface of said core having an annular depression therein adjacent to said wall sections, the latter having inner projections substantially complemental to said depression, and means releasably holding said projections of the wall sections in juxtaposition to said depression.

9. A spark plug as set forth in claim 8, wherein said holding means includes a ring surrounding and in frictional engagement with said wall sections.

10. In a spark plug: a core of insulating material having a pair of opposed ends and adapted to be received with a tubular mounting body having an end face, said core having a nose portion and a tubular extension at one end thereof, said extension being in surrounding, spaced relationship to said nose portion to present an annular recess having an open extremity at said one end of the core, said extension having a lateral projection disposed for covering said end face of the body when said core is received therein.

11. In a spark plug as set forth in claim 10, wherein the outer surface of said core has an annular depression therein for complementally receiving projection means on 7 the inner surface of said body when the latter receives said core.

12. In a spark plug as set forth in claim 10, wherein said core has a first longitudinal portion adjacent to said one end thereof and a second longitudinal portion integral With said first portion and remote from said one end, said second portion having a maximum transverse dimension less than that of said first portion to present a gasket-re ceiving shoulder at the junction between said first and second portions.

References Cited UNITED STATES PATENTS 1,092,322 4/1914 Witter 313143 X 8 1/1915 Ellis 313143 X 11/1917 Linn 313143 X 6/1920 Ingels 313143 X 4/1933 Anderson 313-143 X 1/1934 Anderson 313-143 X US. Cl. X.R. 

